With one known arrangement of this type, the braking member is a brake band made of an unalloyed heat treatable steel, while the brake drum is made of an unalloyed band steel. The braking action of this device is reduced when lubricant penetrates between the friction surfaces and forms a lubricating layer.
In chain saws, the saw chain is driven about a guide bar and must be lubricated with chain lubricating oil during operation to prevent the saw chain from overheating. Accordingly, chain lubricating oil is always present on the guide bar and on the saw chain and, because of the moving chain, some of this oil inevitably reaches the braking interface of the brake drum and the brake band. The presence of lubricating oil at the braking interface reduces the coefficient of friction and increases the time needed to bring the saw chain to standstill.
The braking arrangement of a chain saw must be capable to bring a moving saw chain to standstill in fractions of a second to protect the operator thereof in a dangerous condition such as kickback.